Catalyst System for an Internal Combustion Engine and Method for Producing It

ABSTRACT

A catalyst system for an internal combustion engine with at least one cylinder and/or piston is characterized in that the catalyst is arranged in the form of nanoparticles on the cylinder and/or piston.

The invention relates to a catalyst system for an internal combustion engine and to a method for producing such a catalyst system.

In modern internal combustion engines, particularly in the automobile sector, great attention has been devoted to the problem of removing undesirable components from the combustion gas. In this case, usually, catalysts which are arranged on the exhaust gas side of the engine are employed. However, these catalysts are active mostly only at reduced temperatures, and therefore the efficiency is mostly low when the engine is started. Moreover, catalysts arranged on the exhaust gas side tend to undergo increased corrosion, and the power decreases due to the deposition of chemical components or simply to mechanical wear.

From the abstract of JP 11-223 122 A, it is known, for example, to introduce the catalyst directly into the adjacent outlet tract of the cylinder for combustion gases. Alternatively, a catalyst coating may also be provided, which is applied to the piston or to the cylinder inner walls, so that this coating becomes active in the combustion space formed by the cylinder and the piston.

According to DE 199 45 742 C1, a catalyst which has a metal fiber catalyst body is disclosed for an internal combustion engine. This catalyst may be fixed to the piston, that is to say the catalyst comes into contact with the combustion gases in the combustion space. It is thereby possible, even during combustion, to influence the combustion process catalytically.

According to EP 0 695 859 A1, too, catalyst material may be attached in the region between the piston and cylinder, in such a way that it comes into use in the combustion space of the internal combustion engine during the combustion process.

The object, therefore, is to provide a catalyst system for an internal combustion engine, which has comparatively high efficiency in any operating situation of the engine, along with a long power duration.

This object is achieved by means of a catalyst system having the features of claim 1. Accordingly, a catalyst system for an internal combustion engine having at least one cylinder and/or piston is provided, which is characterized in that the catalyst is arranged in the form of nanoparticles on the cylinder and/or piston.

Nanoparticles are understood, in the context of the present invention, to mean, in particular, particles which have one or more of the following properties:

-   -   a form with diameters of between at least 5 and at most 500 nm     -   a catalytically active surface     -   a material composition which consists of metal, ceramic, glass,         plastic or mixtures of said materials, such as, for example,         metal ceramic or polymer ceramic     -   functionalized surfaces     -   a core shell (that is to say, a core with a casing) or a         multilayer construction.

Arranging the nanoparticles on the cylinder and/or piston results, inter alia, in at least one of the following advantages:

-   -   The efficiency of the internal combustion engine is increased in         that the catalyst is arranged in the combustion space and         therefore can operate at optimal temperature even when the         engine is being started.     -   By arrangement on the cylinder, a more efficient and clean         catalysis can be achieved; as a result, in particular, longer         running times of the catalyst can also be achieved.     -   Since the catalyst is provided in the form of nanoparticles, a         higher catalysis rate per weight of catalyst used can be         achieved, as compared with catalysts according to the prior art.     -   Since no extra catalyst space has to be provided on the exhaust         gas side, a more compact type of construction can be achieved,         thus making it possible, for example, to use the catalyst system         even on motor saws or smaller vehicles, such as mopeds or         motorized bicycles.

According to a preferred embodiment of the invention, the nanoparticles are provided and/or arranged in nanoparticle tubes which possess the approximate form of elongate tubes. This arrangement has proved to be particularly efficient, since particularly good catalysis efficiency can thus be achieved. Preferably, the nanoparticles are provided and/or arranged in aluminum oxide pores or the nanoparticle tubes are designed in the form of aluminum oxide pores.

According to a preferred embodiment of the invention, the mean diameter of the nanoparticle tubes amounts to at least 5 nm and at most 100 nm. The catalysis efficiency can thereby be increased even further. Preferably, the mean diameter of the nanoparticle tubes amounts to at least 10 nm and at most 50 nm, more preferably to at least 12 nm and at most 40 nm and most preferably to at least 15 nm and at most 20 nm.

According to a preferred embodiment of the invention, the mean length of the nanoparticle tubes amounts to at least 5 μm and at most 50 μm. Owing to such a length of the nanoparticle tubes, absorption onto the nanoparticles is increased, and better catalysis is obtained. Preferably, the mean length of the nanoparticle tubes amounts to at least 10 μm and at most 30 μm, more preferably to at least 15 μm and at most 25 μm.

According to a preferred embodiment of the invention, the ratio of diameter to mean length of the nanoparticle tubes amounts to at least 1:300 and at most 1:1500. This has proved to be particularly advantageous in practice. Preferably, the ratio of diameter to mean length of the nanoparticle tubes amounts to at least 1:500 and at most 1:1200, more preferably to at least 1:800 and at most 1:1000.

According to a preferred embodiment of the invention, the mean distance between two adjacent nanoparticle tubes of a cluster amounts to at least 15 nm and at most 20 nm. Good catalysis efficiency, at the same time with a stability of the nanoparticles, is thus achieved.

According to a preferred embodiment of the invention, the nanoparticles are selected essentially from a material from the group comprising Pt, Pd, Rh, Ir, Co, Ni, Cu, Ag, Au, Ru, Ir, Os, Re and mixtures thereof. These materials have proved in practice to be the best materials for the present invention.

According to a preferred embodiment of the invention, the nanoparticles are thermally stable essentially over the entire temperature range of at least 600° C. and at most 800° C.

Lengthy use in internal combustion engines is thereby achieved. In the context of the present invention, “essentially” means at least 50%, preferably at least 70% and most preferably at least 90%. Preferably, the nanoparticles are thermally stable essentially over the entire temperature range of at least 400° C. and at most 900° C., preferably of at least 200° C. and at most 1000° C.

In the context of the present invention, “thermally stable” is understood to mean, in particular, that said materials remain mechanically stable over the temperature range and/or the strength does not change essentially over the temperature range.

According to a preferred embodiment of the invention, the surface/volume ratio of the nanoparticles (on a nanometer scale) amounts to at least 1:1 and at most 1:5. Catalysis efficiency increased even further is thereby achieved. Preferably, the surface/volume ratio of the nanoparticles amounts to at least 1:1.5 to at most 1:4, more preferably to at least 1:2 to at most 1:35, and most preferably to at least 1:25 to at most 1:3.

According to a preferred embodiment of the invention, the nanoparticles are adapted to the surface structure of the cylinder and/or piston.

In the context of the present invention, “adapted” is understood to mean, in particular, that the nanoparticles possess a form and size which, according to the preferred embodiment of the invention described below, can be deposited into the aluminum oxide pores and/or deposit themselves therein.

The invention relates, moreover, to a method for producing a catalyst system which contains nanoparticles, as described above, the cylinder consisting essentially of aluminum. The method is characterized in that the nanoparticles are added during the anodizing of the aluminum and deposit themselves into the surface structure of the cylinder.

In the event that the cylinder consists essentially of aluminum, it has proved advantageous to add the nanoparticles during the anodizing of the aluminum. In the anodizing operation, the surface of the aluminum is oxidized into aluminum oxide, thus resulting in a significant enlargement of the volume, approximately in the region of 20%. The accompanying variation in the structure causes the nanoparticles to deposit themselves in it.

The structural parts mentioned above and also those claimed and those described in the exemplary embodiments and to be used according to the invention are not subject in their size, configuration, choice of material and technical design to any particular exceptional conditions, and therefore the selection criteria known in the field of use may be adopted unrestrictedly.

Further details, features and advantages of the subject of the invention may be gathered from the subclaims and from the following description of the accompanying drawing, in which an exemplary embodiment of the catalyst system according to the invention is illustrated by way of example. In the single drawing:

FIG. 1 shows a diagrammatic perspective illustration with a partially sectional view of a detail of the surface of a highly idealized catalyst system according to a first embodiment of the invention.

FIG. 1 shows a diagrammatic perspective illustration with a partial sectional view of a detail of the surface of a highly idealized catalyst system 1 according to a first embodiment of the invention. In this catalyst system, the surface of an aluminum cylinder 30 has been oxidized by anodizing, so that hexagonal cells 10 consisting of aluminum oxide are formed. It may be noted that the regular arrangement according to the figure is a highly idealized illustration; in actual fact, the diameters, the thickness and the arrangement of the individual cells 10 deviate from one another and form a statistical distribution.

As can be seen in the figure, various pores are formed within the individual cells and form elongate tubes (=the nano-particle tubes 20, as described above). Before anodizing, then, nanoparticles were added according to the present invention, which (not shown in the figure) arrange themselves statistically within these nanoparticle tubes and ensure the desired effect according to the invention. It is particularly advantageous, in this case, if the nanoparticle tubes have the features described above as regards length, diameter and ratio between diameter and length. 

1-9. (canceled)
 10. A catalyst system for an internal combustion engine with at least one cylinder (30) and/or piston forming a combustion space, the catalyst being arranged in the form of nanoparticles in the cylinder (30) and/or on the piston.
 11. The catalyst system as claimed in claim 10, characterized in that the nanoparticles are provided and/or arranged in nanoparticle tubes (20) which are in the approximate form of elongate tubes.
 12. The catalyst system as claimed in claim 10, characterized in that the mean diameter of the nanoparticle tubes (20) amounts to at least 5 nm and at most 100 nm.
 13. The catalyst system as claimed in claim 10, characterized in that the mean length of the nanoparticle tubes (20) amounts to at least 5 μm and at most 50 μm.
 14. The catalyst system as claimed in claim 10, characterized in that the mean distance between two adjacent nanoparticle tubes (20) amounts to at least 15 nm and at most 20 nm.
 15. The catalyst system as claimed in claim 10, characterized in that the nanoparticles consist essentially of a material selected from the group consisting essentially of Pt, Pd, Rh, Ir, Co, Ni, Cu, Ag, Au, Ru, Ir, Os, Re and mixtures thereof.
 16. The catalyst system as claimed in claim 10, characterized in that the nanoparticles are thermally stable in the range of at least 600° C. to at most 800° C.
 17. The catalyst system as claimed in claim 10, characterized in that the surface/volume ratio (on a nanometer scale) of the nanoparticles amounts to at least 1:1 and at most 1:5.
 18. The catalyst system as claimed in claim 10, characterized in that the nanoparticles are adapted to the surface structure of the cylinder and/or piston.
 19. A method for producing a catalyst system as claimed in claim 10, the cylinder consisting essentially of aluminum, characterized in that the nanoparticles are added during the anodizing of the aluminum and deposit themselves into the surface structure of the cylinder.
 20. The catalyst system as claimed in claim 11, characterized in that the mean diameter of the nanoparticle tubes (20) amounts to at least 5 nm and at most 100 nm.
 21. The catalyst system as claimed in claim 11, characterized in that the mean length of the nanoparticle tubes (20) amounts to at least 5 μm and at most 50 μm.
 22. The catalyst system as claimed in claim 11, characterized in that the mean distance between two adjacent nanoparticle tubes (20) amounts to at least 15 nm and at most 20 nm.
 23. The catalyst system as claimed in claim 11, characterized in that the nanoparticles consist essentially of a material selected from the group consisting essentially of Pt, Pd, Rh, Ir, Co, Ni, Cu, Ag, Au, Ru, Ir, Os, Re and mixtures thereof.
 24. The catalyst system as claimed in claim 11, characterized in that the nanoparticles are thermally stable in the range of at least 600° C. to at most 800° C.
 25. The catalyst system as claimed in claim 11, characterized in that the surface/volume ratio (on a nanometer scale) of the nanoparticles amounts to at least 1:1 and at most 1:5.
 26. The catalyst system as claimed in claim 11, characterized in that the nanoparticles are adapted to the surface structure of the cylinder and/or piston. 